It is common medical practice to deliver nutritional fluids either enterally through the alimentary canal via a naso-gastric tube or a jejunostomy catheter, or parenterally via an intravenous catheter. Medical personnel generally utilize positive pressure pumps to deliver and regulate the flow of these nutrients.
Conventional enteral pumps are non-volumetric, positive-pressure peristaltic systems utilizing silicone rubber tubing inserts, which are in direct contact with the pump rotor, and which, in turn, are mechanically connected to the PVC tubing linking the fluid reservoir and patient to the pump. The silicone rubber insert is stretched around the rotor by means of mounting tabs which are positioned in slots or brackets on the pump face. The tubing sets also embody drip chambers which are mounted inside optic path housings in order to observe the passage of fluid drops, thereby detecting nutrient flow or the absence of flow.
The intrinsic design of these peristaltic enteral pumps results in a number of functional drawbacks, most notably: volumetric inaccuracies under many common operating conditions, unsafe operating conditions if the set is not properly mounted on the pump, and complicated set assembly techniques.
The accuracy of peristaltic pumps is greatly affected by the pressures exerted by the fluid reservoir and patient height relative to the pump, by the fluid viscosity, and by the physical properties of the silicone insert. These are non-volumetric systems, as compared to positive displacement volumetric systems such as syringe pumps, and do not embody valving systems, which results in exogenous pressures affecting the overall flow rate. The use of expensive silicone rubber inserts has been necessary in order to maintain accuracy and avoid deterioration and splitting of the tubing over even relatively short periods. The silicone tubing must be extruded to very tight inner diameter and outer diameter tolerances and requires very precise cutting and overall length assembly within the mounting tabs.
The assembly process is further complicated because silicone is not compatible with plastic bonding techniques. This problem also creates the possibility of leakage at the attachment joints if the set is pressurized due to a downstream occlusion. The mounting of these sets has always been an acknowledged problem. Patients and medical personnel have often incorrectly mounted the sets on the pump face resulting in no flow, inaccurate flow, or in some cases, even open flow, which may cause severe patient complications. The mounting of the drip chambers within optic path housings is also an acknowledged problem, resulting in false alarm situations. The use of optic path flow detection also restricts the use of these pumps to relatively upright, motionless applications; otherwise, the fluid drops may bypass the optics beam, or may splash on the side walls and coat the walls, falsely blocking the optics beam.
Many parenteral drop flow controllers or infusion pumps are susceptible to the same types of problems as the enteral pumps. Even the more advanced, expensive, positive-pressure, volumetric syringe types perform in less than a satisfactory manner in several respects. These devices are generally complicated to operate, and allow for incorrect mounting of the disposable cartridges. These problems are documented and have even been the subject of discussion in new patent applications.
The major obstacle to proper mounting of the cartridges is the attachment of the syringe head to the pump piston mechanism. This design restriction has been documented to cause misalignment, which may even allow air or pathogens to enter into the syringe fluid chamber, as well as to cause inaccurate flow rates. It has also been reported that various valving mechanisms and alarm detector interfaces have been improperly mounted in the pump bodies.
A second major limitation of these devices is their lack of appropriateness for enteral nutritional administration. Generally these devices and the disposable cartridges are very expensive compared to enteral products, and require sophisticated trained personnel for proper operation. In addition, several cartridge designs allow for the accumulation of enteral nutrient residue in the valving inlets/outlets, which over time will adversely affect the flow rates and volume delivered.
As a result of the current state-of-the art limitations of the enteral and parenteral nutrient pump systems, a clear need exists to provide the medical community with an accurate, safe, cost-effective system which may be reliably utilized by relatively unsophisticated patients and personnel in a wide range of settings, including ambulatory and home care. The invention set forth below intrinsically fulfills this need.